Nitrogen-doped carbon quantum dots fabricated from cellulolytic enzyme lignin and its application to the determination of cytochrome c and trypsin

Exploring the Characteristics of Carbon Structures Obtained from LignoBoost Lignin

In the present study, carbon structures from LignoBoost lignin were synthetized using HNO3/H2SO4 one-pot hydrothermal treatment, followed by a thermal treatment. The obtained compounds were characterized using different techniques, such as FTIR, DVS, DLS, XRD, fluorescence imaging and STEM. The formed LCMs presented graphitized structure with quasi-spherical shapes. All obtained materials presented negative values of zeta potential due to the charge from the hydroxyl and carboxyl groups, as confirmed by XPS analysis. All the data obtained sustained the heterogeneous composition of the lignin-based carbon materials, which arise from the complex structure of lignin. Fluorescence imaging demonstrated the potential of the materials as optical imaging agents.

Pyrolytic Lignin: A Promising Precursor for the Green Synthesis of Fluorescent Carbon Nanoparticles

This study presents a simple and cost-effective approach for synthesizing pyrolytic lignin-based carbon dots (CDPLs) via controlled thermal pyrolysis in water. To the best of our knowledge, this is the first time that pyrolytic lignin has been used as a precursor for carbon dots. The one-pot method produced blue/green fluorescent CDPLs with an average size of 34 nm and a negative surface charge of -10.4 mV. The characterization techniques revealed the optical properties and chemical composition of CDPLs, with a fluorescence quantum yield of 7.9%, which is comparable to those of lignin-derived carbon dots. The decay lifetime of CDPLs was in the nanosecond range, which is typical for carbon dots. This study demonstrates the potential of using pyrolytic lignin, a lignocellulosic byproduct, to produce carbon dots through a simple and reproducible method, contributing to the development of sustainable carbon-based nanomaterials.

Carbon Dots: A Review with Focus on Sustainability

Carbon dots (CDs) are an emerging class of nanomaterials with attractive optical properties, which promise to enable a variety of applications. An important and timely question is whether CDs can become a functional and sustainable alternative to incumbent optical nanomaterials, notably inorganic quantum dots. Herein, the current CD literature is comprehensively reviewed as regards to their synthesis and function, with a focus on sustainability aspects. The study quantifies why it is attractive that CDs can be synthesized with biomass as the sole starting material and be free from toxic and precious metals and critical raw materials. It further describes and analyzes employed pretreatment, chemical-conversion, purification, and processing procedures, and highlights current issues with the usage of solvents, the energy and material efficiency, and the safety and waste management. It is specially shown that many reported synthesis and processing methods are concerningly wasteful with the utilization of non-sustainable solvents and energy. It is finally recommended that future studies should explicitly consider and discuss the environmental influence of the selected starting material, solvents, and generated byproducts, and that quantitative information on the required amounts of solvents, consumables, and energy should be provided to enable an evaluation of the presented methods in an upscaled sustainability context.

State-of-the-art of lignin-derived carbon nanodots: Preparation, properties, and applications

Lignin-derived carbon nanodots (LCNs) are nanometer-scale carbon spheres fabricated from naturally abundant lignin. Owing to rich and highly heritable graphene like π-π conjugated structure of lignin, to fabricate LCNs from it not only endows LCNs with on-demand tunable size and optical features, but also further broadens the green and chemical engineering of carbon nanodots. Recently, they have become increasingly popular in sensing, bioimaging, catalysis, anti-counterfeiting, energy storage/conversion, and others. Despite the enormous research efforts put into the ongoing development of lignin value-added utilization, few commercial LCNs are available. To have a deeper understanding of this issue, critical impacts on the preparation, properties, and applications of state-of-the-art LCNs are carefully reviewed and discussed. A concise analysis of their unique advantages, limitations for specific applications, and current challenges and outlook is conducted. We hope that this review will stimulate further advances in the functional material-oriented production of lignin.

Photoluminescent Transparent Wood with Excellent UV-Shielding Function

At present, light transmission, energy saving, environmental protection, and UV-shielding materials are very important for optimizing indoor living environment. Here, a fluorescent transparent wood (FTW) with UV-shielding function was prepared by encapsulating a carbon quantum dot and epoxy resin into a delignification wood template. FTW exhibits excellent optical transmittance (about 91%), water absorption stability (weight gain rate less than 9%), longitudinal tensile strength (139 MPa), and UV-shielding properties. Due to the photoluminescence characteristics of the carbon quantum dot and the natural cellulose skeleton of wood, FTW can show uniform luminescence under ultraviolet lamps. At the same time, it has remarkable UV-shielding performance. This kind of photoluminescent transparent wood with a UV-shielding function also has the potential to be applied to fields such as electromagnetic shielding and harmful gas detection.

Recent developments in lignin-based fluorescent materials

Biomass-based fluorescent materials are an alternative to plastic-based materials for their multifunctional applications. Lignin, an inexpensive and easily available raw material, demonstrates outstanding environment-responsive properties such as pH, metal ions, dyes sensing, bioimaging and so on. To date, only a little work has been reported on the synthesis of lignin-based fluorescent materials. In this review report, synthetic approaches and light-responsive applications of lignin-based fluorescent carbon dots and other materials are summarized. The results reveal that lignin-based fluorescent carbon dots are prepared by hydrothermal method, exhibit small size <10 nm, reveal significant quantum yield, biocompatibility, non-toxicity, photostability and display substantial tunable emission and can be efficiently employed for sensing, bioimaging and energy storage applications. Finally, the forthcoming challenges, investigations, and options open for the chemical and/or physical modification of lignin into fluorescent materials for future applications are well-addressed. To our knowledge, this is the first comprehensive review report on lignin-based fluorescent materials and their light-responsive applications. In addition, this review will attract remarkable consideration and thrust for the researchers and biochemical technologists working with the preparation of lignin-based fluorescent materials for broad applications.

A Fluorescence Biosensor for Tyrosinase Activity Analysis Based on Silicon-Doped Carbon Quantum Dots

Tyrosinase (TYR) plays a pivotal role in the biosynthesis of melanin, and its activity level holds critical implications for vitiligo, melanoma cancer, and food nutritional value. The sensitive determination of TYR activity is of great significance for both fundamental research and clinical investigations. In this work, we successfully synthesized silicon-doped carbon quantum dots (Si-CQDs) through a one-pot hydrothermal method with trans-aconitic acid as carbon source and N-[3-(trimethoxysilyl)propyl]ethylenediamine as the dopant, exhibiting remarkable fluorescence quantum yield (QY) and photostability. Correspondingly, Si-CQDs were used as a probe to construct a sensitive, rapid, and user-friendly fluorescence method for TYR detection. The method relied on the oxidation of isoprenaline (ISO) by TYR, where Si-CQDs were employed as a highly efficient probe. The testing mechanism was the internal filtering effect (IFE) observed between Si-CQDs and the oxidative system of ISO and TYR. Under the optimized conditions, the fluorescence strategy exhibited a detection range of 0.05-2.0 U/mL for TYR with a limit of detection (LOD) of 0.041 U/mL. Furthermore, we successfully demonstrated the accurate determination of TYR levels in human serum, showcasing the promising potential of this method in various practical scenarios.

Lignocellulosic Biomass-Based Carbon Dots: Synthesis Processes, Properties, and Applications

Carbon dots (CDs), a new type of carbon-based fluorescent nanomaterial, have attracted widespread attention because of their numerous excellent properties. Lignocellulosic biomass is the most abundant renewable natural resource and possesses broad potential to manufacture different composite and smart materials. Numerous studies have explored the potential of using the components (such as cellulose, hemicellulose, and lignin) in lignocellulosic biomass to produce CDs. There are few papers systemically aiming in the review of the state-of-the-art works related to lignocellulosic biomass-derived CDs. In this review, the significant advances in synthesis processes, formation mechanisms, structural characteristics, optical properties, and applications of lignocellulosic biomass-based CDs such as cellulose-based CDs, hemicellulose-based CDs and lignin-based CDs in latest research are reviewed. In addition, future research directions on the improvement of the synthesis technology of CDs using lignocellulosic biomass as raw materials to enhance the properties of CDs are proposed. This review will serve as a road map for scientists engaged in research and exploring more applications of CDs in different science fields to achieve the highest material performance goals of CDs.

A turn-off fluorimetric -aptasensor for early detection of apoptosis inside the cells

To detect cytochrome c (Cyt c) as an important biomarker of apoptosis inside the cells, a simple, label-free, fluorometric detection method has been presented. For this purpose, an aptamer/gold nanocluster probe (Aptamer@AuNCs) was produced which could specifically bind to Cyt c leading to fluorescence quenching of AuNCs. The developed aptasensor showed two linear ranges of 1-80 μM and 100-1000 μM and a detection limit of 0.77 μM and 297.5 μM, respectively. This platform was successfully used to assay Cyt c release inside the apoptotic cells and their cell lysate. Aptamer@AuNC due to its enzyme-like properties could replace antibodies in Cyt c detection by conventional blotting techniques.

Carbon dots derived from peptone as "off-on" fluorescent probes for the detection of oxalic acid

A simple and rapid microwave heating approach was reported for the preparation of water soluble carbon dots (CDs) using peptone as carbon source with the assistance of ethylenediamine. Several characterization techniques such as transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) were employed to analyze CDs. The optical properties of synthesized CDs were examined by UV-vis and fluorescence spectroscopy. The CDs exhibit strong blue emission under 365 nm UV lamp and have the excitation and pH (2.0-12.0) dependent emission behavior. The fluorescence intensity of CDs can be selectively quenched by Co²⁺ via dynamic mechanism, while the addition of oxalic acid (OA) results in a remarkable recovery of the fluorescence intensity due to the strong coordination binding between oxalic acid and Co²⁺. Hence, the prepared CDs can conveniently serve as "off-on" fluorescent probes for highly sensitive determination of oxalic acid. The wide linear range is 0.5-70 mg/L with a low detection limit of 0.288 mg/L. Furthermore, the probes were successfully applied to detect oxalic acid in tomato and cherry tomato samples with the recovery of 96.4 %-106.4 % and the relative standard deviation lower than 0.25 %.

Recent advances in lignin-based carbon materials and their applications: A review

As the most abundant natural aromatic polymer, tens of million of tons of lignin produced in paper-making or biorefinery industry are used as fuel annually, which is a low-value utilization. Moreover, burning lignin results in large amounts of carbon dioxide and pollutants in the air. The potential of lignin is far from being fully exploited and the search for high value-added application of lignin is highly pursued. Because of the high carbon content of lignin, converting lignin into advanced carbon-based structural or functional materials is regarded as one of the most promising solutions for both environmental protection and utilization of renewable resources. Significant progresses in lignin-based carbon materials (LCMs) including porous carbon, activated carbon, carbon fiber, carbon aerogel, nanostructured carbon, etc., for various valued applications have been witnessed in recent years. Here, this review summarized the recent advances in LCMs from the perspectives of preparation, structure, and applications. In particular, this review attempts to figure out the intrinsic relationship between the structure and functionalities of LCMs from their recent applications. Hopefully, some thoughts and discussions on the structure-property relationship of LCMs can inspire researchers to stride over the present barriers in the preparation and applications of LCMs.

Biomass-Derived Carbon Dots and Their Sensing Applications

Carbon dots (CDs) can be widely used in the field of sensing because of its good water solubility, low toxicity, high fluorescence stability and excellent biocompatibility. It has become a popular trend to prepare high-value, inexpensive, renewable and environmentally friendly CDs sensors from biomass resources. This article reviewed the research progress of biomass-derived CDs as chemical, physical and biological sensors in recent years and studied their preparation processes and sensing abilities. Furthermore, the prospects and challenges of biomass-CDs sensors were discussed. This article is expected to provide inspirations for the design, preparation and application of biomass-CDs sensors in the future.

Quantitative detection of captopril in urine by smartphone-assisted ratiometric fluorescence sensing platform

Captopril (CP) is a widely used antihypertensive drug. In this study, a smartphone-assisted sensing platform on the basis of ratiometric fluorescent test strips was developed, which can accomplish visualization for the quantitative detection of captopril. Ratiometric fluorescent probe was constructed from carbon dots (CDs) and gold nanoclusters (Au NCs). After adding Cu²⁺ to fluorescent probe, Cu²⁺ can complex the amino and carboxyl groups on the surface of Au NCs and aggregate Au NCs, which will quench the fluorescence of Au NCs. Compared with amino and carboxyl groups, -SH in CP has a higher affinity for Cu²⁺ and can capture Cu²⁺ to restore Au NCs fluorescence. In this process, CDs remained essentially unchanged as background fluorescence. As CP concentration increased, the fluorescence color showed a distinct change from blue to purple to orange. Based on this principle, a sensing platform combining smartphone and fluorescent test strips was constructed to visualize the quantitative detection of CP by RGB values. Under optimal conditions, the wide linear range of CP detection for both fluorescence spectrometer and smartphone paper-based sensing platform was 0.25-50 μM. The limits of detection were as low as 76 nM and 101.3 nM, respectively. Furthermore, it was implemented successfully for the detection of CP in urine. The satisfactory recoveries were 96.0-103.3% and 92.0-108.0% for fluorescence spectrometer and smartphone platform, respectively. This smartphone-assisted platform provided a new approach for visual detection of CP, which showed its great potential in bioanalytical assays.

A novel fluorescence ratio probe based on dual-emission carbon dots for highly selective and sensitive detection of chlortetracycline and cell imaging

The novel dual-emission carbon dots (DECDs) for highly selective and sensitive recognition of chlortetracycline (CTC) and cell imaging were synthesized successfully by one-step synthesis. The obtained DECDs possessed two fluorescence peaks (345 nm and 450 nm) and showed specific response to CTC, resulting in a decrease in fluorescence intensity at 345 nm, a blue shift, and an increase in fluorescence intensity at 450 nm. The obtained DECDs exhibited highly selective response to CTC and not to its analogues, such as tetracycline, doxycycline, and oxytetracycline. Thus, an excellent ratiometric probe for the detection of CTC was fabricated successfully and used for the detection of CTC in real samples with the detection limit (LOD) of 16.45 nM. More importantly, the DECDs were used for quantitative detection of CTC in living cells, which demonstrated excellent biocompatibility and broad prospects in biomedicine application. Finally, the excellent selectivity of DECDs toward CTC was attributed to the FRET mechanism and the formation of complexes.